Exporting all shader node with object to import into another scene
You should not use the import/export tools when copying stuff from one scene to another. Use the Append tool in your big scene (File->Append) and choose the bread .blend file. Then navigate to the "Objects" folder in the .blend file and select all objects belonging to your loaf of bread. This will import it with all materials applied.

The alternative is to first open the bread .blend, select the bread and press Ctrl + C and then paste it into an other file opened with Ctrl + v